Patent literature 1: JP 2013-126822 A
Conventionally, an electric power steering device that uses a motor as a drive source is disclosed. For example, patent literature 1 discloses an electric power steering device (also, referred to as a motor-driven power steering device). In the electric power steering device, an axial force applied to a steering shaft is estimated based on values from a torque sensor, a current sensor, and motor rotational angular speed detecting means, and the estimated axial force is used in a program for improving steering feeling.
The inventor of the present disclosure has found the following.
When sensor abnormality which includes the abnormality of the torque sensor, the current sensor, or a rotational angle sensor is detected, a predetermined time for confirming the abnormality as a malfunction after an initial detection of the abnormality is required to avoid an erroneous determination. In the electric power steering device in patent literature 1, a sensor abnormality is not taken into consideration. Thus, an axial force is estimated using a low-reliability sensor value during a period of time from the detection of abnormality until the confirmation of malfunction.